Table 1.

Percentage of Missouri Adolescent Female Twin Study participants reporting each risk and outcome of interest, stratified by race/ethnicity

Variable	European Americans	African Americans	Statistical test	pa
Low parental monitoring	21.1%	30.4%	χ2(1) = 21.41	P < .001
Substance use characteristics
Alcohol initiation	94.4%	86.2%	χ2(1) = 47.62	p < .001
Alcohol use ≤ 14 years old	24.8%	16.4%	χ2(1) = 17.48	p < .001
Mean age at alcohol initiation,	16.1 (2.8)	17.1 (3.2)	F(1,1914) = 32.47	p < .001
in years (SD)
Tobacco initiation	75.6%	67.8%	χ2(1) = 14.20	p < .001
Tobacco use ≤ 11 years old	15.6%	14.2%	χ2(1) = 0.65	p = .46
Mean age at tobacco initiation,	13.9 (3.3)	14.2 (3.7)	F(1, 1624) = 2.40	p = .12
in years (SD)
Cannabis initiation	51.9%	56.6%	χ2(1) = 3.91	p = .08
Cannabis use ≤ 14 years old	9.6%	12.4%	χ2(1) = 3.96	p = .08
Mean age at cannabis initiation,	16.5 (2.6)	16.7 (2.8)	F(1, 1274) = 0.46	p = .50
in years (SD)

Notes: Low parental monitoring was defined as the lowest quartile on the parental monitoring score distribution. Significant values are in bold type.

^ap values adjusted for the nonindependence of twin pairs.